Field of the Invention
The present invention relates to the association of an organic dispersion of iron particles and of a detergent within a composition notably useful as a fuel additive for internal combustion engines.
Description of the Related Art
During combustion of fuel and notably of gas oil in an engine, the carbonaceous products tend to form carbonaceous particles, which will be designated in the following of the description under the expression of “soots”, which are said to be noxious both for the environment and for health. For a long time, there has been a search for techniques with which the emission of these soots may be reduced.
A satisfactory solution consists of introducing into the exhaust line a particle filter (or PF in the following of the text) which will block soots in its channels in order to let a gas escape without any soots. When a certain amount of accumulated soots in the PF is attained, the soots are burned in order to free the channels of the PF. This step for regenerating the PF is usually accomplished at greater temperatures than the temperature of the gas during normal operation of the engine, the soots usually burning in air at temperatures above 650° C.
In order to assist with regeneration of the PF, a catalyst is generally used which has the purpose of facilitating oxidation of the soots either directly or indirectly. By facilitating the oxidation of the soots is meant the fact of allowing their oxidation at a lower temperature so that this temperature is attained more frequently during normal operation of the engine. A portion of the soots may thus be continuously burned during the operation of the engine.
The catalyst also gives the possibility of lowering the temperature required for regenerating the PF so that the regeneration temperature is less than the combustion temperature of the soots without the presence of said catalyst. The catalyst also allows acceleration of the oxidation rate of the soots which allows a reduction in the required time for regenerating the PF.
The use of an additive for assisting with regeneration of the PF, vectorized by the fuel feeding the engine or further a fuel borne catalyst (FBC), proved to meet many criteria since it allows regeneration of the PF more rapidly and at a lower temperature than the competing technology called catalyzed soot filter (CSF, the catalyst being immobilized in the PF), which contributes to reducing fuel consumption for regenerating the PF (and thus reducing CO2 emissions).
New engine technologies, such as diesel engines with a common-rail system and high pressure direct fuel injection, are performing but however sensitive to fuel quality. It is notably known that deposits may notably form in injectors of diesel engines during their operation. The amount of deposit and their rate of formation depend on the quality of the fuel used in the engine but also on the nature of the fuel additives present in the latter.
By <<fuel additive>> is meant here any additive allowing improvement in the distribution of the fuel in the engine and/or improvement in the operating performances of the engine and/or improvement in the operating stability of the engine over time. Fuels which contain unstable components, like fatty acid methyl esters generally present in biofuels, tend to form more deposit than mineral fuels not containing any of them.
Further, the presence of certain metals in fuels like copper or zinc may lead to increased amounts of deposit and thus to exacerbated fouling levels of the injectors. The metals present in fuels stem from various origins like the metals stemming from the contact between the fuel and the fuel distribution network or from any other contamination. Metals may also be deliberately introduced into the fuel like in the case of metal additives for assisting regeneration of the PF. Even if these additives are beneficial for regeneration of the PF and are thus desirable, some may promote the formation of deposit in the fuel circuit and most particularly in fuel injectors.
Deposits may lead to a loss of power of the engine and may possibly go all the way to damaging the engine. These deposits may also degrade the quality of the combustion in the cylinders and lead to an increase in polluting emissions and in engine fuel consumption. It is known that detergent additives reduce or suppress formation of deposit in the injectors.
Among fuel additives for assisting with the regeneration of the PF, dispersions of rare earths, notably based on cerium, and/or iron are known to be efficient for regenerating the PF and contribute to the reduction of the oxidation temperature of the soots. These dispersions should have good dispersibility, high stability over time and sufficient catalytic activity at a relatively not very high concentration in the fuel into which they are introduced.
The dispersions known to this day do not always meet all these criteria. They may have for example good dispersibility but not sufficient stability, notably when they are introduced into fuels containing fatty acid methyl esters or another easily oxidizable fuel of vegetable origin. These dispersions may be sufficiently stable but may have catalytic activity at too high metal concentrations for them to be economically of interest. Moreover, as indicated earlier, all these dispersions should have a limited impact on the operation of fuel injectors, notably to lead to limited fouling of the latter, even in the presence of a fuel containing biofuel or further a fuel containing metals. Further the presence of an FBC in the fuel may lead to a reduction in the oxidation resistance of the fuel, notably when it contains biofuels.